This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A348421 #12 Oct 20 2021 07:12:34 %S A348421 47,67,107,127,151,167,179,227,239,263,283,307,347,367,431,439,467, %T A348421 487,491,503,547,571,587,599,607,643,647,683,719,727,739,751,787,811, %U A348421 823,827,887,907,947,967,983,991,1019,1031,1051,1063,1087,1103,1163,1187 %N A348421 Primes p == 3 (mod 4) such that (p+3)/2 is not prime. %C A348421 Complement of A092109 with respect to A002145. %H A348421 Jianing Song, <a href="/A348421/b348421.txt">Table of n, a(n) for n = 1..10000</a> %F A348421 a(n) = 2*A348423(n) - 3. %e A348421 47 is a term since it is a prime congruent to 3 modulo 4 and (47+3)/2 = 25 is composite. %t A348421 Select[4*Range[0, 300] + 3, PrimeQ[#] && ! PrimeQ[(# + 3)/2] &] (* _Amiram Eldar_, Oct 18 2021 *) %o A348421 (PARI) isA348421(n) = isprime(n) && (n%4==3) && !isprime((n+3)/2) %Y A348421 Cf. A002145, A092109, A348423. %K A348421 nonn,easy %O A348421 1,1 %A A348421 _Jianing Song_, Oct 18 2021